​Speaker –  Richard Fiorella, University of Utah, Bio (hosted by Carli Arendt)

Seminar Title –  Linking source to sink: how water vapor isotope ratios improve our understanding of hydrologic processes

Abstract – Stable water isotope ratios are a widely used geochemical tracer of both modern and past water cycle processes. Phase changes in the water cycle unequally partition the isotopologues of water (most commonly ¹H₂¹⁶O, ¹H²H¹⁶O, and ¹H₂¹⁸O) and as a result, the isotopic composition of precipitation is thought to reflect an integrated of history of that water from its evaporative source until it leaves the atmosphere as precipitation. However, variation in precipitation isotope ratios can be plausibly related to either changes in local conditions such as temperature, remote conditions such as the source location of the moisture, or both. As a result, interpretations of precipitation isotope ratios are often ambiguous and would be improved with better mechanistic methods linking precipitation isotope ratios to the underlying hydrologic processes.

At the same time, advancements in spectroscopy have allowed for the routine measurement of vapor isotope ratios. Traditionally, measurements of water vapor isotope ratios were both labor intensive and low resolution. As such, many models developed to interpret isotope ratios in archives such as of lakes, leaf water, and tree rings assume that atmospheric water vapor is in isotopic equilibrium with local precipitation. As measurements of vapor isotope ratios become more widespread, a new picture is emerging where this assumption is rarely satisfied outside of precipitation events. In this talk, I will show how incorporating water vapor isotope ratios and numerical modeling techniques can help to improve our interpretation of isotope ratios in the water cycle using examples in both natural and urban environments.

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